In certain devices, such as surgical instruments, it is desirable to store energy within the instrument to facilitate firing the instrument. One such device is a clip applier disclosed in U.S. Pat. No. 4,611,595. This clip applier stores energy in a spring which is retained by a latch mechanism. Movement of a handle disengages the latch resulting in rapid and uncontrolled release of the stored energy to actuate the clip applier. However, in some instruments it would be desirable to have structure for allowing for a controlled release of the stored energy to control the rate of actuation of the instrument.
Further, many surgical instruments, such as 60 mm staplers used in thick tissue, require more energy than can be comfortably developed by a single squeeze of a human hand. Currently, surgeons may use two hands to fire, or use instruments which require multiple, lower effort squeezes, to fire. Thus, it would also be desirable to have a surgical instrument that can be pre-energized by pumping at least once and possibly several times to store potential energy in a spring. This pre-energizing may be done by a surgical nurse or other assistant. This is particularly important during long procedures where fatigue, from multiple firings, may be uncomfortable to the surgeon.